1. Field of the Invention
The present invention relates to an ion implantation apparatus and a method of controlling the ion implantation apparatus.
2. Description of the Related Art
In a semiconductor production process, a step of implanting ions to a semiconductor wafer (hereinafter, referred to as an “ion implantation step”) is generally performed for the purpose of changing the conductivity and the crystalline structure of the semiconductor wafer. An apparatus that is used in the ion implantation step is called an ion implantation apparatus, and has a function of forming an ion beam ionized by an ion source and accelerated and a function of carrying the ion beam to an implantation processing chamber and irradiating the ion beam to a wafer inside the processing chamber.
The ion implantation apparatus has a configuration in which, for example, an ion source, a drawn electrode, a mass-spectrometry magnet, a mass-spectrometry slit, an acceleration/deceleration device, a wafer processing chamber, and the like are disposed along the beam line and ions are implanted into a wafer as a semiconductor substrate. These devices control the ion beam by using an electric field formed between the electrodes to which a voltage is applied or a magnetic field generated by the magnet.
Further, the implantation processing chamber is provided with a plasma generation device that prevents the wafer surface from being charged by the implantation of the ions. The plasma generation device neutralizes the charges charged to the wafer surface by supplying plasma to the wafer surface. As such a plasma generation device, for example, a discharging mechanism that generates plasma by causing a discharge in the introduced source gas is provided inside the implantation processing chamber.
The plasma generation device needs a small amount of the quantitative source gas for generating the plasma during the plasma shower action. Particularly, since a large amount of the source gas is introduced during the plasma ignition period compared to the case of the plasma shower action, the vacuum degree of the implantation processing chamber is degraded, and a large amount of the source gas also partially flows into the beam line connected to the implantation processing chamber. When the ion beam having acceleration energy collides with the source gas while the ion beam is carried along the beam line, the source gas is ionized, so that charged particles are generated. For this reason, the charged particles are generated in the middle of the beam line into which a part of the source gas flows. Since the beam line is provided with an electrode to which a high voltage is applied, the generated charged particles flow into the electrode so that a load current is generated, and hence there is a concern that an overcurrent may be generated in a power supply connected to the electrode.